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Winfrith Atomic Energy Establishment was built for the construction and operation of experimental and research reactors.[1] Construction began in 1957, and the first low-energy reactor (ZENITH) was completed and in operation by the end of 1959.[1] This was quickly followed by two others (NESTOR) in 1961 and (DIMPLE) in 1962.[1] The last reactor was shut down in 1995, although decommissioning of the site will not finish till 2021.[2] Winfrith housed several experimental reactors during its lifetime. There were also impact test facilities, and a used nuclear fuel examination facility with the associated hot cells.

Experimental reactors included:

ZENITH (Zero Energy High Temperature Reactor) built in 1959. It was a zero-energy reactor which was used to study the physics of high temperature reactors.[3]

NESTOR (Neutron Source Thermal Reactor) built in 1961. Based on the JASON reactor operated by the Hawker Siddeley Nuclear Power Corporation at Langley, Berkshire.[4] NESTOR was a small research reactor which produced a large amount of neutrons making it a useful tool for investigating the design of power-producing reactors and carrying out sub-critical experiments on core assemblies.[4]

DIMPLE (Deuterium Moderated Pile of Low Energy) built in 1962. Originally built at Harwell in 1954, Dimple was Britain's first heavy water reactor.[5] It was moved to Winfrith in 1962 and extensively modified and rebuilt for studies of the physics of reactor systems moderated by light or heavy water and by an organic moderator.[6]

ZEBRA (Zero Energy Breeder Reactor Assembly) built in 1962. Designed for studying the neutron physics of a wide variety of fuel assemblies containing uranium and plutonium.[7]

HECTOR (Hot Enriched Carbon-moderated Thermal Oscillator Reactor) built in 1963. Designed to examine the suitability of various materials for use in power reactors.[8]

JUNO, built in 1964. Built from the components of a zero-energy graphite moderated reactor called NERO, and from a sub-critical assembly used for steam generating heavy water reactor investigations, it was used to provide the information needed for the design of small power reactor cores.[9]

Dragon. The Dragon reactor was built in 1964.[1] It was the first power reactor built at Winfrith.[1] It was an experimental reactor built as a European inter-governmental research and development project.[1] It was the first demonstration high-temperature gas-cooled reactor (HTGR) and had a thermal output of 20 MW. It operated until 1976.

The largest reactor at Winfrith was a steam-generating heavy water reactor (SGHWR) commonly known as the Winfrith Reactor.[1] It was designed by the UKAEA, and was intended to combine the features of the CANDU reactor and PWR.[10] The core consisted of a bank of metal pressure tubes (zirconium alloy) which passed through vertical tubes in a tank of heavy watermoderator – allowing the designers to do without the pressure vessel that normally contained the reactor's core.[11] The pressure tubes contained the fuel which was cooled by a flow of light water up the tubes, generating steam.[11] The fuel was slightly enriched uranium.[11] The power level was varied by the level of the moderator.[12] The reactor exported up to 100 MW of electric power to the National Grid.[11] For many years it was the largest water cooled reactor in the United Kingdom.[1]

Construction of the reactor began in 1963.[1] It began operating in 1967,[12] and was notable for being built within the allotted timescale (four years), and for being under-budget.[13] It was built as a demonstration reactor,[12] with the intention of building a series of commercial reactors based on the design.[10] However, the SGHWR design was never advanced beyond the prototype at Winfrith,[12] and the design was sidelined in favour of AGR reactors.[10] The Winfrith reactor was shut down in 1990.[12]